Micro-tensile and TEM analysis of thermally aged Ni-Mo-Cr alloy before and after alpha particle irradiation

GH3535, a candidate Ni-Mo-Cr alloy for GEN IV molten salt reactors, is thermally aged at 650 degrees C for 2000 h and exposed to low density so they ion irradiation. The ion energy is attenuated via means of a degrader wheel to vary between 0.1 to 5MeV, resulting in a near -uniform level of radiation damage over a 10 mu m depth to a dose of 0.25 dpa and helium concentration 1250 appm at room temperature. A focused ion beam (FIB) milling machine was used to fabricate micro-tensile samples (5 x 5 mu m in cross sectional area and 17 mu m in length) from pre- and post- irradiated GH3535 samples. Some of the micro-tensile samples feature a single crystal whilst others feature a grain boundary. Both single crystal and grain boundary micro-tensile results showed helium irradiation had a negligible effect on tensile strength and elongation illustrating the radiation damage resistance of thermally aged GH3535. Additionally, the grain-boundary micro-tensile samples did not fail along the grain boundary before irradiation nor after irradiation which suggests GH3535 continues to fail trans - granularly even after helium ion irradiation. TEM and EBSD analysis were performed on the unirradiated and irradiated aged GH3535 samples and the results of the analysis are discussed here in relation to the micro-tensile results.